The present invention is especially concerned with the provision of an improved arrangement for what will be referred to as the series twin seam welding of sheet metal panels. In this particular welding process, a pair of side panels may be simultaneously welded to opposite side edges of a central panel, this process being frequently employed in the fabrication of sheet metal housings or cabinets. Conventionally, in the prior art, twin seam welding has been accomplished by rolling a pair of disc electrodes along the overlapped edge portions of the panels while the panels are clamped upon a support table. The central panel of the group being welded has been relied upon to complete the electrical circuit between the two points of welding. Because the panels are normally of a substantial area, a substantial dissipation of current occurs within the central panel. The power supply carriage in such systems rolled on rubber wheels which functioned to press the central panel down. Prior to the filing of the present application a patentability search which was conducted uncovered the following patents.
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